The structure and functional organization of several interrelated structures of the basal forebrain and anterior temporal lobe will be studied in the rat and monkey. The structures to be studied include the amygdaloid complex, the largely cholinergic nucleus basalis and diagonal band nuclei, the ventral striatum and pallidum, the olfactory and entorhinal cortices, and other cortical areas of the anterior temporal lobe. However, the major emphasis in this grant period will be on the medial, magnocellular part of the mediodorsal thalamic nucleus (MDm) and the orbital and mesial parts of the frontal cortex, which are tightly interconnected with each other by thalamocortical and corticothalamic fibers, and which both receive inputs from the basal forebrain and anterior temporal lobe. All together, these structures form a complex associative system, which has been implicated in memory processing as well as in forebrain control of visceral mechanisms, and is involved in such neurological disorders as epilepsy, autism and Alzheimer's disease. In order to analyze and correlate the connections between these structures, and especially to analyze the afferent fibers to MDm and the functional subdivisions of the orbital and mesial cortex, several anterograde and retrograde axonal tracers will be used. These include 3H-leucine, phaseolus vulgaris leucoagglutinin (PHA-L), WGA-HRP, and the fluorescent dyes "true blue", "fast blue", "diamidino yellow" and "fluorescent gold", as well as the "transmitter specific" tracers 3H-D-aspartate and 3H-GABA. In most cases two or more tracers will be combined, in order to label and compare different fiber systems in a single experiment. In addition, electrophysiological recording of responses to olfactory bulb stimulation will be used to map the olfactory related area of the orbital cortex, and to guide the placement of microinjection of the axonal tracers.